Gene therapy targeted to the central nervous system (CNS) offers a promising treatment approach for neurological disease. Gene delivery vectors based on adeno-associated virus (AAV) have emerged as a promising platform capable of efficiently delivering therapeutic genes to the CNS in a variety of neurological disease models and in phase I clinical trials. However, experimental success with AAV has relied on the direct injection of viral particles into the neural tissue, which is a highly invasive procedure that places limitations on vector dissemination. Intravenous administration of AAV would be more clinically feasible, but the serotype commonly employed in gene therapy is unable to efficiently penetrate the blood-brain barrier (BBS). The goal of this proposal is to design improved AAV vectors that efficiently disseminate into the CNS following intravenous administration. It is hypothesized that AAV vectors that efficiently transmigrate across the BBB can be selected and evolved from a library of AAV mutants using library screening and directed evolution techniques according to three specific aims: Aim 1. Measure the efficiency with which natural AAV serotypes cross the BBB. A panel of AAV serotypes will be studied for their ability to cross the BBB in both an in vitro BBB model as well as following intravenous administration in vivo. Aim 2. Evolve AAV mutants that efficiently and selectively transmigrate across brain capillary endothelial cells. A library of AAV mutants will be generated and subjected to iterative rounds of selection and mutagenesis to generate a population of AAV variants that efficiently cross the BBB. Aim 3. Evaluate the ability of selected AAV mutants to bypass the BBB and transduce cells in the CNS following intravenous administration. Selected AAV mutants will be analyzed for their ability to transduce cells in the CNS. The biodistribution of AAV and the resulting transduction profiles will be analyzed. Relevance: There is a need for minimally-invasive treatment options for neurological diseases such as Alzheimer's and Parkinson's disease. The proposed research is concerned with the development of gene carriers that can migrate from the patient's bloodstream to the brain to treat diseased neurons.